Contour tracing apparatus



June 7, 1960 R. H. EISENGREIN 2,939,368

CONTOUR TRACING APPARATUS Filed May 12, 1958 5 Sheets-Sheet 1 "'Yor +vyTEMPLAT E H Fig.3

ZERO REFERENCE NT 90 20b 21 S5 23 AC. EXITATION\ I \/x=vcose To XAxIsAMPLIFIER FIXED WINDING f 270 FI' q. 4

Vy 1V, n e INVENTOR.

TOYAXS ROBERT H. EISENGREIN.

AMPLIFIER g fiTM I ATTY- June 7, 1960 R. H. EISENGREIN 2,939,358

CONTOUR TRACING APPARATUS Filed May 12', 1958 5 Sheets-Sheet 3 @mg m (DT T E O I Fl g.8

vx+Vy I LLI 3 4o 5 l J 3 RESOLVER ROTOR ANGLE Q [-i 1;. 9a .5 270 350 3I \RELAY INVENTOR.

ROBERT H. EISENGREIN June 7, 1960 R. H. EISENGREIN CONTOUR TRACINGAPPARATUS 5 Sheets-Sheet 4 Filed May 12, 1958 RESOLVER SHAFT AXISECCENTRIC ARM STYLUS AXIS I 1 T REFERENCE POINT 1 TEMPLET EDGELINVENTOR.

ROBERT H. ERSENGREIN.

June 7, 1960 R. H. EISENGREIN 2,939,368

CONTOUR TRACING APPARATUS Filed May 12, 1958 5 Sheets-Sheet 5 MANUAL VxV cos a CONTROL EXITATION CONSTANT I 50 WINDING voms E AC SOURCE VY VS'N9 SE TACHOMETER MOTOR SPINDLE RESOLVER' T P(-VX) 3 C) 3!" \/Y W E Q(\/X)g R(VY) \/v E V -E I T( v) F! g. l5 E i INVENTOR.

ROBERT H. EISENGREIN.

United sta s Patent CONTOUR TRACING APPARATUS Filed May 12, 1958, Ser.No. 734,513

' 3 Claims. (CI. 90-135 invention relates to apparatus by which adesired pattern contour or profile may be exactly or proportionatelyreproduced by a cutting or grinding unit under the control of aprofile-scanning device and a pair of angularly-disposed but coactingservo-motors.

In the preferred form of the invention, either angular orliueardisplacement of the scanning device by contact with the patternactivates one or the other or both ofthe servo-motors and causes them tochange the position of the cutting or grinding unit relative to aworkpiece which is to be machined to the desired contour.

To the attainment of this general object, an improved scanning device isprovided which will selectively activate the servo motors in accordancewith changes in its orientation which are caused by changes in theengaged contour of the pattern.

In the preferred construction, the servo-motors operate alongperpendicular axes and move proportionately to the coordinates of thescanning device in anygiven position.

In the modified construction, the servo-motors are controlled from atape or other similar record which presents the desired contour insuitably coded form.

The invention further relates to arrangements andcombinations of parts,which will be hereinafter described and more particularly set forth inthe appended claims.

A preferred form of the invention is shown in the drawings, in whichFig. 1 is a plan. view of a pattern or contour template to bereproduced;

Fig. 2 is an axis movement diagram to be described;

Fig. 3 is a diagrammatic view of certain assembled tracing apparatus;

Fig. 4 is an exploded view of the several parts of a resolver;

2,939,368 Patented June 7, 1960 as that shown in the template of Fig. 1.The apparatus will produce this contour by tracing a mechanical templatewhich presents the contour, or from coded information supplied by apunched tape or card.

The tracing apparatus to be first described uses a mechanical templateas a reference, and a cutting tool is associated with the tracingapparatus and will reproduce the desired contour in any suitableworkpiece.

To trace thecontour, a stylus 10 (Fig. 1) is attached; eccentrically tothe shaft 11 of a rotary sensing device or resolver 12. The resolver canbe moved independently along both the X and Ydirections, as shown by theset of coordinate X and Y axes (Fig. .2). w

a result of the stylus movement causing rotation .of the resolver shaft,the sensing device or resolver 12 supplies electrical information to theX and Y servo- 1 drives. The resulting X and Y axis movements make theFig. 5 is a diagram showing voltage reactions to various angulardisplacements of the resolver;

Figs. 6a to 6e indicate directions of tool movement responsive todifferent voltage vectors;

Fig. 7 is a diagram illustrating electric or tape control;

Fig. 8 is a diagram showing superposed voltage curves;

Fig. 9 is a diagram showing certain combined voltage curves;

Fig. 9a is a diagram of an additional voltage curve;

Fig. 10 is a diagram of a control loop to be described;

Fig. 11 is a diagram of the desired movement of a tool when turning acorner;

Fig. 12 is a similar view to be described;

Fig. 13 is a diagram showing stylus reactions to a simple template;

Fig. 13:: is an enlarged diagram of certain parts in Fig. 13;

Fig. 14 is a diagram of a control loop involving variable spindlespeeds;

Fig. 15 is a diagram showing use of a network of resistors; and i Fig.16 is a perspective view of a stylus adjusting device.

The apparatus to be described automatically traces the'progressivechanges in a desired 360 contour, such stylus always maintain continuouscontact with the template and move in a direction tangent to thetemplate edgeat the point of contact.

For example, assume the stylus 10 is initially in the position 0(Fig. 1) and away from the template 20. By holding the stylus in thecorrect position, it will cause the X and Y servo-drives to move thestylus toward the template. Initially only X axis motion is needed. Uponcontacting the template 20, the reaction torque of the.tem-. plate onthe stylus 10 will oppose a stylus bias torqueof the control motor 14(Fig. 10), and the stylus will be forced to partially rotate, thuschanging the X and Y orders to be given to the servo-drives. The styluswill continue to move -angularly until the X motion is 'zero and the Ymotion becomes maximum.- At this point, the stylus motion will betangent to the template at point a. I As the contour continues tochange, the stylus bias torque will cause or permit the stylus to beshifted angularly by the template reaction torque. This displacementWill cause appropriate changes in the X and Y velocities until theresulting velocity produces a stylus movement tangent to the contour atthe new point of stylus contact.

Progressive angular positions of the stylus with respect to the templateare shown at position b and c in Fig. 1. General construction Thegeneral construction is shown diagrammatically in Fig. 3. A resolver 12has a stylus 10 eccentrically attached to one end of its shaft 1'1, anda control motor 14 is attached to the other end of the shaft 11. Theseparts are all mounted on an X axis slide 19.

The shaft 11 of the resolver 12 is turned to various positions bycoaction of the control motor or stylus bias torque and any templatereaction torque caused by the pressure of the template 20 against thestylus 10. As the resolver shaft 11 is turned by the stylus, theresolver furnishes electrical signals for the X and Y servo-drives.

15 and 16. Since the resolver 12 is mounted on the X1 axis slide 19,mechanical feedback from the X axis slide 19 to the stylus causescontinuous movement of the X and Y servo-drives until the entireapparatus is traveling: in a path tangent to the contour of the templateat the point of stylus contact.

A base or table 17 (Fig. 3) supports a Y axis slide 18, a servo-drive 16and an amplifier A. An X axis slide 19, a servo-drive 15 and anamplifier A2 are mounted on top of the Y axis slide. Anything mounted onthe Y axis slide 19 can thus be moved to any point in a single plane bythe independent motions of the X and Y servo-drives 15 and 16. Theamplifiers A and A2 pro vide increased power for the servo-drives.

Any suitable tool T may be mounted on the X slide 19. The template 20ais mounted on afixed support in sa imam that the stylus 180 pointdifferent fromthe. 0 pointf.

lfthse electtical' voltages are used to servo-drives Which-provide anoutput speed directly-pro portional to the electricalsignal andadirectionof rota- The electrical details of the resolver 12 are shownin Fig. '4. The resolver has a rotor 20* which is given a continuousbias, as a fixed winding 21 of the resolver is excited with an AC.voltage V. V g The resolver 12 has two output windings 22 and 23arrangedso that one winding 23 furnishes a signal V where. V ='V cos 6;0 is' the angle. of the resolver rotor 20 withrespect to a zeroreference point on the nonrotating casing of the resolver.

Fig. '5 shows how V' and V will vary as the resolver i may be turnedfrom the zero reference point to various,

angular positions up to a full 360", and'this cycle may in fact bethereafter repeated. 1

7 With the arrow on the resolver'rotor 20 at the 'Zero' referencepoint,(as shown in Fig. 4) 0' equals zero.

Therefore, Vy=V sin 0 =O and V '=V cos 0=='V.- As

the angle 0 increases towards ,90", V increases and V decreasesuntil at90, V =V and V -=0. As the angle 7 ;6 increasesfurther, V -and V vary asshown in the curves. When 0:180, V -=V cos 180{=V. At this point,'the

minus sign signifies that the voltage amplitude is the f'same as. it waswhen 69:0; but its phase is 180? from the original value. -lt is thisphase; reversal'which' makes the "'ntrol table tiondirectlyproportional'to' the phase of" the signal (that is, clockwise rotationffo'r plus V' and counter-clockwise rotation for Y voltages)', thevertical scale of Fig. 5

can be converted to'show table velocity'directly', Any suitable servodrives may be used, such for instance as are lshown in Small PatentsNos. 2,585,507 and By'c'ombining' the X and Y"velocities for" variousresolver rotor positions, as shown in Fig. 6, it appears thatthere'sultin'g 'velocityVR has a magnitude which remains constant but adirection which 'vari'es directly with the.

resolver rotor angle 6. V t V This result can be shown mathematically bythe equation below.

neglect velocity VR V Vsin0 .1 1

Tan J .Tan cos Tan .l'lanfi]. 6 If for'each point on the templatecontour, the resolver rotor 20 were turned by an angle-equal to theangle of the tangent at that point, the resolver would: produce theelectrical signals to control the table drives mentioned above. Thesesignals; would'- then produce a resulting velocity vector which at allwouldhave constant magnitude and also a direction equal to the tangentof the contour at the point of stylus contact, 7

.Mechanical actuation oftha'resoluer I 7 'Means to; actuate; theresolver rotor; mechanically is.

7 shown in Fig.3. One end of the -resolver rotor shaft 11 is connectedtoa control motor 14. The other end "aseaeearj,

it] can contact all edges of 25 this notation.

The magnitude-of the velocity vector VR I isthe square root of the sumof the squares of V and is eccentrically offset from the rotor shaftaxis. Fig. 1 shows a' typical template 20- and the various positions ofthe stylus and rotor axes needed to provide the velocity vector VR, sothat the template edge will be traced.

With thestylus initially away from the template at point 0, the controlmotor torque locks the resolver rotor 20 at the zero reference point.'Fig. 5 shows that the system then provides, X velocity and zero Yvelocity" and that the'stylus will be moved toward the 10 template 20. ti a t When the stylus-first contacts the template, the resolver shaft 11begins to rotate, because the eccentricity of the stylus producesuareaction torque on this shaft. This 7 reaction wr 'ue causes'partial'rotation of the resolver 15 shaft and the change. in' the anglefl from,zero towards 90 eventually causes V to become zero,'and V to becomea'maximum. a -S imultaneously,-the slide velocities become zero in theX'dir'ect ion; in theYhir'ection. is shown bythe position of the; stylusand 'the'eccent'ricity atthe point a in Figj'l. t 7 As the templatereaction force increasesas a result of this initial'movement against thetemplate and as the "resolver rotor is thusforced to turn, the apparatussenses At ajpredete rmined angle of from this zero reference, theapparatus automaticallyswitches a new voltage to the control motor 14,so that," instead of locking the resolver rotor in the zero referencepositi'on, it now produces a constant'bias torque, as shown at positiona'of Fig. 1 and maintains this position until the template curvaturechanges, as shown at the first corner of-the templatei Thelbias torquethen forces the resolver shaft 11 to turn clockwise to the positionshown a at b? In actual practice, this change gradual and continuous.'The changes inrthe angle 0 alfect both V andfV so that the resultingvelocitiesare always cor feet and insure accurate tracing ofthetemplate.

' The dotted line around the template shows the actual path tobe'followed by the stylus The eccentricity '40 is showninexaggerated-form and the resolver and stylus are only slightlydisplacedfin practice. As the apparatus continues to trace the template20',

the bias torque will again force theresolver/ to turn at thenex t corneruntil 9=270. This angle causes 'V to equal V sin 270=V,1and V to equalVi cos 270=0. This reverses the Y axis slide drive from the directionshown at a... V v V 1 At the-nextcorner 1,? the contourchangesgraduallyand the biastorque forces the stylus 10 and the resolver 59 shaft 11toturn gradually. The angle 0 is varied from 270 at the corner toward180. The X and, Y axes slide velocities also change. gradually betweenpoints 11" and 'e on the template.

At. the point e,. an abrupt change in contour causes the template toexert a torque opposing the bias torque, and the resolvershafit is. thusforced back toward the 270 position. At the-point f, thebias torqueforces the'resolver to return tothe 180 position. This results 60 in Vbecoming 0, and V becoming ofmaxirnum negative value; 7

The apparatus next follows the template from f to Electrical or tapecontrol of the resolver In addition to controlling the resolver bytracing the mechanical template, the control may be electrical, and

the position of the resolver shaft may beQdeteImined by control motor.torque alone. This mode'of. control performs two functions. First, itpermits locking the resolver at such anangle that the resulting V and Vsignalswill cause. the. servo-drives to move (the tool to approachthework from. a fixed direction. Secondly,it

permits the resolver angle to be thereafter set at unique anglesindependent of a mechanical template.

The way in which the control motor positions the resolver rotor is bestexplained by referring to Fig- 5. For a resolver rotor angle position of180, the voltage V is zero. If the rotor is turned towards 270, Vincreases in the negative direction; but if the rotor angle decreasestowards 90, V increases in a positive direction. By sensing the amountof this minus or plus shift of V from zero, and also by sensing thephase change (positive or negative), it is possible to tell how far andin which direction the control rotor has turned.

By amplifying this voltage and feeding it to a control motor attached tothe resolver shaft, the motor can be made to turn the resolver rotor ina direction which always reduce V to zero. Thus, it would lock the rotorat the 180 position, and if the rotor is forcibly turned from thisposition, V will increase in a direction which would amplify the voltageon the control motor and would causeit to actto resist this change.

This electrical system of operation is shown diagrammatically in Fig. 7.As V becomes'positive because the resolver rotor angle 6 decreasestowards 90, the amplified value of .V (namely, KV causes the resultingcontrol motor torque to return the rotor to the 180 position. At thispoint, V becomes zero. and the control motor torque likewise is zero.For further movement of the rotor towards 270, the voltage and torqueare both reversed.

7 It is important to note that V is also zero at the rotor position of0. However, this is an unstable operating position, since the slope ofvoltage versus rotor angle is reversed from that found at the 180 point.

For example, if the rotor is at a point just 01f 0", as at the 10position, the voltage V is positive, and a positive voltage will causethe control motor to increase the resolver angle. Therefore, the rotorwill move from the 10 point towards larger values. Thisfurther'increases V and causes the resolver rotation to continue untilthe apparatus finally stops at the 180 point.

If the voltage V is fed into the electronic amplifier K instead of V thecontrol motor will be forced to rotate the resolver until a new positionis reached, at which point V will equal 0., This will occur at aresolver angle of either 90 or 270. But only at the 90 point is theslope of voltage versus resolver angle suitable for stable operation.Therefore, the rotor should remain locked at the 90 position, and shouldresist movement from this position by control motor torque.

Fig. 8 shows how additional locking angles may be obtained by taking thevoltages V and V and reversing their phase through a transformer. Theresulting curves are as shown.

It is thus apparent that the criteria for locking the resolver rotor atdifierent angles is to develop a voltage in the electronic amplifierwhich is zero at some unique rotor angle. This voltage must alsoincrease in the posi tive direction'as' the rotor angle'is decreased, asfrom 90 towards 0. The voltage must also increase negatively as theresolver angle is increased, as from 0 to 90".

With V and V available in Fig. 8, conditions exist for providing rotorangles of 270 and 0 respec tively. By feeding V into the electronicamplifier (Fig.7), the control motor will lock the resolver rotor at270. .By switching in V,., the control motor will lock the resolverrotor at 0. There are thus four unique positions in which the resolverrotor can be locked, namely 0", 90, 180 and 270. These locking anglesare achieved by switching the voltages V V V and -V respectively intothe electronic amplifier K.

Additional resolver locking angles To lock the resolver rotor at anglesother than those mentioned above, it is only necessary to feed a voltageto the electronic amplifier which meets the above-mentioned criterion ofbeing zero and which also has the correct voltage slope with respect tothe rotor angle.

On inspection of the curves of Fig. 8, it appears that adding thevoltage V and V will develop a resulting voltage curve 40 which varieswith the resolver angle, as shown in Fig. 9. This curve meets thedefined criterion only at a rotor angle of 135. By feeding this sum of Vand V into the electronic amplifier K, the control motor will lock therotor at 135 Several unique combinations are attainable by mixing V V--V and V as shown in the table below:

Add: Locking angle, degrees V and --V 5 V and V 135 -V and V 225 l-V and-V 315 A further refinement of locking angle is achieved by combiningpercentages of V 'and V... In Fig. 9, each point of the curve V +V isachieved by adding the dividing both sides of the equation by V cos A wehavevAt 135, V and V are sin A cos A- .Tan A: P A=arc Tan (P) The finalequationshows that the angle A at which PV -l-V equalszero depends onthe percentage (P) of V which is used. As P varies from 0% to A variesfrom 180 to Using a selected percentage Q of V namely, QV and writingthe same equations as above, the following results are obtainable:

V +QVy=V cos A-l-QV sin A=0 or p Tan A Q Now as Q varies from 0 to 100%,A will vary from 90 to 135.

Other combinations of V V V and V;., plus varying percentages of each,provide a locking position for any angle in the full 360. Thus, byswitching into the electronic amplifier the correct magnitude and amountof the various V and V combinations, the control motor can bemade tolock the resolver rotor at an unique angle in 360.

Electrical approach and mechanical actuation To provide a mechanicalapparatus with the ability to approach the template from a selectedangle, the resolver rotor will be locked at such selected angle, aspreviously discussed. The resulting V and V signals, when fed to theslide servo-drives, will cause the stylus to move towards the templateat this selected angle. Assuming that V is being fed to the resolvercontrol motor, this will cause the resolver to be locked at 0. Referringto Fig. 1, this would represent the stylus as at the point 0. When V andV are now fed to the slide servo-drives, the only motion resulting wouldbe X motion, since V =V, and V =0. 4

i in the negative direction; The control motor torque will resist thetemplate reaction torque, but since'the' servodrives exert a morepowerful force than the resolver control motor, the resolver rotor willbe turned. .When this "voltage -V reaches a predetermined level V as at-45? discussed under fMechanic'alActuation of Resolver.

: Auton iatic rrttcing with' outmecha ltical template 7 Inorder toautomaticallytrace' 'a particular-contour 'without a mechanicaltemplate. each p'oint on the contour which presents a unique angle mustbe definedL-It is also "know that for each unique resolverangle the com-I bination of V and Ya when fed to theservo-drives, will cause allpoints on the X'axisslidetoirnhve at this unique angle. As previouslyexplainedQtlie cohtrol motor can lock the resolver rotor at any uniqueangle'byswitching in resolver control motor-voltages of correctmagnitude and phase. 7 Referring to the contour shown: in'Fig. 1, thepath to be followed at point a? is defined by an angle of 90.

time signals 'could be determined by an electronic pulse generator,orbyi a synchronous motor, with a cam and switch which would producepulses at definitejntervals.

, :The voltage for the resolvercontrol" motor always comes from.the'resolver' windings producingV and V sistors such as shown inFig.15, there would always be available alluniquervoltages needed togenerate any angle.

Assume that it is desired to resolve a 360 contour into 1". intervals,then 360 separ'ate A.C. voltages would be needed. a

By using a punched tape with enough coded holes to feed any selectedvoltage of the 360 available A.C. voltages to the resolvercontrol'motor, the tool would be made to' travel in adirectiondetermined by any of these uniqueang1es.- a V Referring again-to Fig.12'', 'the tool will operate at the angle defined by point 1. for a timedetermined by the pulse generator; When a new'pulse is generated, thepunched tape would be' rapidly advanced by its tape drive mechanism;'The'new' positionwouldrepresent the correctcombination's of codedholeswhich-would. switch a 7 new; A.C. voltage to the controlmotor'sothat the angle If V is fed to the resolver control motor,- theresolver rotor will be locked at 90; thus, V willequal O andV will equalV. Only Y motion will be generated ahd the contour along a will bereproduced.

Sensing and measuring either distance or time to be traveled in this Ydirection will determine how long to 'utilize'this V signal. 'Ameasurement of time in this [Whenthe'travel along thepoint fit contourlhas reached the cornenthe resolver control motor will be energized by VThe resolver rotor will now be locked at an angle of 0? and Y axismotionceasebut X axis motion will be generated to produce the contour repre-'sented by point b. The indicated measurement of distance or timewillagain determine when the next contour change Will be reached- Atthispoint V will excite the resolver control motor and'lock the resolverrotor at 270. A further indication of required distance or time willagain determine the length'of contour travel.

, At each of the corners, of course, the voltage tothe resolver controlmotor must he shifted gradually to generate the dotted outer curve shownin Fig. 11. By following'the dotted curve, the cutting to'ol'will cut a'square corner. a

The rate at which new voltages must befed 'to the" control motor willdepend on the accuracy with which the final curve must be'ge'nerated,and also uponthe rateat which the curvemust be generated. Fig.111represents an expanded portion of a corner contour and illustrates thedesired curve, plus an error zone which defines the limits of error.which can be tolerated. 7

By selecting a number of points in the desired curve, which member isdetermined by the-error limits, a unique angle of travel can bedetermined for each selected point. The final rate at which the curvemus't'be generated'will determine the length of time-each'of theseunique angles of travel'must be maintained. Byfeeding the correct A.C.resolver voltage to uniquely define'each. angle represented by thepoints 1, 2, 3, 4, 5, etc. (Fig.12), the resolver rotor angle and theangle of slide travel will be defined. The distance traveled at eachpoint can be controlled by varying the length of time'ea'ch' A.C. signalis fed to the resolver controlimotor; The spacingof-these of point 2'would be generated. This motionwould contime uritil' the next pulse wasgenerated; the tape would again: advance and: furnish a new A.C. voltagewhich represents point3. This process would be repeated for the entirecontour- By thus representing each unique point of a contourbyanAQvoltage-and causing the coded punched tape to feedjthisvoltage tothe resolver control motor for a time determined by the path length anderror limitations, the apparatus can he made to generate any contour,independentlyof any mechanical template.

1 7 V, Eccentricity adjustment .Another added feature of this system isits ability to correctfortvariationsfin cutter'tool diameter. This isimportant, since variations in tool. diameter will cause variations inthe dimensions-of a piecebeing machined. This feature is shown in'Fi'g;13, whichrepresents' a simple rectangular template 20a. styluscenter andthe resolvershaft axis must be in the various positions shown.The'dotted line around the template-indicates the path described bythe'r'esolver axis and is'marked x. This will-be the same path followedby the cutting edge or point'of thetool. f When following a particulartemplate dimension L as shown in Fig. 13, the eccentricity of thejstylusand the stylus diameter D will causethe path x traced by the resolveraxis to give us a resultingdimension, L- which may be defined'a'sbelowz' L,=L [%'e sin (1) where 'y is the angle between the tangenttothe surface traced and the eccentric arm. The'angle -y is normally about45. Since the tooldiameter D is finite, the final dimension L cut by thetool will'be defined as below:

D is constant but D varies asthe tool wears or toground. If e variesover therange'of wear ofD the condition L =L will obtain when To produceslightly over-size or slightly under-size parts, the constantv 0.707 may-be'slightly decreased or slightly increased.

Means foradjusting the eccentricity of the stylus 10 relative to theresolver shaftl l is shown in Fig. 16 and comprises an eccentric-bushing10a for the stylus, which To trace this template, the

bushing is angularly adjustable in an arm 10b and may be secured inadjusted position by a clamping screw 10c. The eccentricity of thissystem is however quite small in actual practice; usually .020" to.040". Since the tool wear is usually no more than .00 to .010", theeccentricity can easily accommodate these variations.

Removal of excess material For particular situations in which thecutting tool cannot remove all of the material in one pass, the systemcan be modified to permit removal of steps of material. Equation 3 aboveshows that L, is a function of L D, and D,. If D is made larger than thenormal size for exact duplication, it is apparent that L; will begreater than the original template dimension and an oversize duplicateof the template will result. The stylus diameter D, may easily beincreased by substituting a stylus of increased dimension, D -l-d. Thiswill increase the work size by 11/2. The value of d to be selected willdepend on the amount of stock which can practically be removed at onecut by the cutting tool.

Conslant cutting feed control loop A special control loop (Fig. 14)permits direct control of cutting feed, that is, the advance inthousandths of an inch per revolution of the tool (or of the work, ifthe work rotates).

For a fixed r.p.m. of a tool, as N, the actual advance of the tool alongthe work is directly proportional to the vector velocity R of V, and V,.For all cases, R=V, the excitation voltage of the resolver fixed phase.

Now feed may be defined as R/N where R is in inches per minute and N isin revolutions per minute. Since R=V, feed may be rewritten as V/N ininches per revolution. By controlling V, which changes the excitation ofthe resolver, the feed can be controlled.

V can be controlled manually, or it can be controlled automatically asshown in Fig. 14, by inserting an autotransformer 50 between a constantvoltage A.C. source 51 and the resolver excitation winding 52. Theautotransformer knob 54 may be directly calibrated in inches perrevolution and may be manually controlled.

In cases where the spindle r.p.m. varies, an automatic control loop(Fig. 14) may be used to compensate for such spindle r.p.m. variations,so as to maintain a constant feed. By mounting a tachometer 60 on thetool spindle 62, there is available a voltage V, directly proportionalto spindle r.p.m. N.

By comparing the voltages V, and V, their difierence V may be obtained.Vg can then be used to excite a servo-motor 64 and thus shift theauto-transformer 50 until V becomes zero.

By correctly calibrating this control loop, the autotransformer voltageoutput V will vary as the spindle r.p.m. N. A constant feed in inchesper revolution is thus provided.

V =K N and V=K V, where K1+Kg are calibration constants. Then Feed==%==kiK:= u F,

K is a constant which is independent of spindle speed.

Conclusion The general construction and operation is fully set forth anddescribed in the preceding pages. and with reference to the accompanyingdrawings.

In the construction controlled by mechanical template contact, a stylusis angularly shifted about its eccentric axis by such contact, and theangular displacement of the stylus efiects changes in operation of oneor the other or both of the two servo-motors which control the movementsand positions of an associated tool.

Special provision is made to compensate for tool wear, and additionalprovision is made to vary the over-all size of the finished workpiece inpre-arranged proportion to the pattern.

With tape or record control, the servo-motors are responsive to codedsignals emanating from a tape or record which carries a desired patternof movements, duly controlled as to time and direction.

Having thus described my invention and the advantages thereof, I do notwish to be limited to the details herein disclosed, otherwise than asset forth in the claims, but what I claim is:

l. Contour-tracing apparatus having, in combination, a template, asupporting structure for a tool or workpiece, a pair of cooperatingservo-motors efliective to move said structure selectively along X and Ycoordinates, a sensing device directly and yieldingly engaging thecontour of said template, and operating control connections between saidsensing device and said servo-motors, and said control connectionsincluding a small control motor and an associated resolver whichtogether apply yielding pressure to hold said sensing devicecontinuously against said template in all relative angular positionsthereof and with a substantially constant bias torque.

2. Control tracing apparatus having, in combination, a template, asensing device initially in a relatively remote position, automaticmeans to advance said sensing device to directly engage the template,and automatic means to thereafter shift the sensing device angularly bydirect and mechanical template contact and in continuous engagement toindicate an exact contour to be reproduced.

3. In a contour-tracing apparatus having a template, a supportingstructure for a tool or workpiece and a pair of cooperating servo-motorsto move said structure selectively along X and Y coordinates, thatimprovement which comprises a sensing device initially held ininoperative position, means to move said inoperatively-positionedsensing device toward the template along a selected and predeterminedline of approach to contact position, and means to thereafterautomatically displace said sensing device by mechanical engagement onlywith the template to indicate an exact contour to be reproduced.

References Cited in the file of this patent UNITED STATES PATENTS2,388,555 Kuehni et al. Nov. 6, 1945 2,622,616 Humes Dec. 23, 19522,627,055 Calosi Jan. 27, 1953 2,679,620 Berry May 25, 1954 2,723,598Mann Nov. 15, 1955 2,786,396 Wetzel Mar. 26, 1957 2,813,461 Schmid Nov.19, 1957 2,814,239 Lavieri et a1. Nov. 26, 1957

